It is known that polyacrylic alkali metal salts have a prominent remedial effect against peptic ulcers (see for example British Patent No. 1435630). In use of such salts alone for human beings, it is hardly possible to administer them orally in the form of powder because of their too strong adhesive nature. Also, even if they could be administered, they are likely to form an undissolved lump in the stomach and can hardly spread and adhere sufficiently to the mucous membranes of the stomach and duodenum, so that such salt substance must be given at a high dose for inducing a significant effect. Therefore, it is more preferable to give said salt substance in a form dissolved in water, but actually, this mode of administration is impractical because more than 20 hours are required for this substance to get dissolved uniformly in water.
There is also known an easily water-soluble granular polyacrylic alkali metal salt preparation obtained by contacting powder of a polyacrylic alkali metal salt with water in a hydrophilic organic solvent, crushing the obtained masses into aggregated granules of desired size (aggregates of primary particles of polyacrylic alkali metal salt), and then coating the granules with a water-soluble polyethylene glycol or a polyoxyethylene derivative which is solid at normal temperature, or with a mixture thereof and a higher fatty acid which is solid at normal temperature, or with such higher fatty acid alone (Japanese Patent Laid-Open No. 133251/75). However, this granular preparation has a drawback in its use as a digestive ulcer remedial medicament as it needs to use the coating agent in an amount of more than 20% of the amount of the base polyacrylic alkali metal salt because otherwise the granules, when administered, could cling to each other to form undissolved lumps, resulting in reduced solubility of the substance in the stomach or duodenum.
In view of the above, the present inventors have devoted themselves to the study for working out a medicinal preparation of polyacrylic alkali metal salts which can produce a high remedial effect against digestive ulcers and which is easy to administer and can be also produced on a commercial scale, and as a result, it was found quite unexpectedly that if such polyacrylic alkali metal salt substance is first granulated according to a proper method and then the obtained granules are coated with a water-insoluble but water-permeable coating agent, said granules when contacted with water, are quickly swollen and dissolved in water to form a uniform viscous solution, allowing easy obtainment of the desired coated granules. This discovery breaks away from the conventional conception that use of an easily water-soluble coating agent is essential for obtaining water-soluble granules.